1. Field of the Invention
The present invention generally relates to controlling downlink transmission timing in communication systems.
2. Description of Related Art
An expanded effort is underway to support the evolution of the Universal Mobile Telecommunications System (UMTS) standard, which describes a network infrastructure implementing a next generation Wideband Code Division Multiple Access (W-CDMA) air interface technology. A UMTS typically includes a radio access network, referred to as a UMTS terrestrial radio access network (UTRAN). The UTRAN may interface with a variety of separate core networks (CN). The core networks in turn may communicate with other external networks (ISDN/PSDN, etc.) to pass information to and from a plurality of wireless users, or user equipments (UEs), that are served by radio network controllers (RNCs) and base transceiver stations (BTSs, also referred to as Node Bs), within the UTRAN, for example.
One set of issues being addressed by the 3rd Generation Partnership Project (3GPP), a body which drafts technical specifications for the UMTS standard and other cellular technologies, includes UTRAN synchronization issues. The 3GPP technical specifications have attempted to address each of these issues. One of these issues is called time alignment handling. In the UMTS standard, time alignment handling is used to control downlink transmission timing at the CN nodes, in order to minimize buffer delay in a serving RNC (SRNC), which is an RNC serving one or more Node Bs. A time alignment handling procedure is controlled by the SRNC.
Although the current time alignment handling procedure for UMTS provides a procedure to control variable delay jitter conditions so as to provide a continuous information stream from the CN through the radio link to a UE, algorithms for triggering timing control and for controlling buffer capacity are not specified. Additionally, there is no mechanism in the time alignment handling procedure for controlling when a downlink transmission is to be transmitted.